You sure it's a design "deficiency" as opposed to just wear and tear?? At any rate, you will (at most) only need to change this part once in your car's life time. Mine is pushing 11 years old, 130k miles and I've verified it's super tight, noise free, and holds vacuum very well. ///MPR77 had 293k miles on his when he replaced it as PM and even his orginal DISA was still going strong.

What's this deficiency you speak of? In that light, every other part on our cars have a "deficiency."

What's its deficiency? The fact that the DISA can blow up the motor when it fails. That's a very poor design.

Wear and tear failure would a singular failure mode, for example the vacuum failing, so the DISA flaps around but doesn't disintegrate.